Big Blue CTO Carbon Block Replacement Water Filters 4 pcs 4.5" x 20" Cartridges Replacement filters for Amazon item B01AR1IPRG or any standard size 20" Big Blue Housing 4 Big Blue Carbon Block Filters (5 micron). Standard size filters 4.5x 20 These can used for residential and commercial applications. Effectively eliminates many impurities from tap water to offer sparkling clean and great tasting water throughout your whole house. All our filters individually wrapped for freshness and protection while in shipment.